The invention relates to apparatus for the transformation of mechanical vibrations into electrical impulses, and more particularly to a magnetic phonograph pick-up cartridge for reproduction of sound or visual images from recorded disks.
Electromagnetic phonograph pick-up cartridges conventionally include a fixed assembly portion and a replaceable assembly portion, the replaceable portion generally including a stylus which may become worn or damaged during use. Frequently, the replaceable portion includes a stylus magnet which is pivotally mounted within an enclosure. The fixed portion is adapted to hold the enclosure and includes magnetic sensing poles which have associated sensing coils for converting magnetic flux changes into electrical signals. Movement of the stylus magnet caused by the stylus tracking recorded grooves on the phonograph disk result in magnetic flux changes inducing electrical signals in the sensing coils. A typical problem with magnetic phonograph cartridges has been in providing a means whereby the delicate stylus/shank/magnet assembly can be replaced while still maintaining high pick-up sensitivity which is related to the degree of magnetic coupling between the stylus magnet and pole pieces. High pick-up sensitivity allows a reduction in stylus magnet mass, which in turn provides reduced stylus tip impedance and a lower tracking force. Minimizing the air gap between magnet and pole pieces, and thus minimizing magnetic reluctance, is one obvious way to increase sensitivity. Some conventional replaceable assemblies have the stylus magnet in an enclosure which can be slidably received by the sensing pole tips. However, the thickness of the enclosure containing the stylus magnet adds to the reluctance of the pick-up cartridge and reduces magnetic coupling and sensitivity. In other replaceable assemblies, sensing poles have been divided into two portions, one portion being removable in conjunction with the stylus magnet and the other portion containing the sensing coils. However, such cartridges typically have the removable pole portion outside of, or colinear, with the non-removable pole portion, and the stylus magnet located between the removable and non-removable pole portions, thereby resulting in a bulky unit having an unacceptably large vertical tracking angle. In addition, mechanical tolerance build-up between the sensing pole portions have necessitated larger magnets to provide adequate magnetic flux across larger air gaps between the magnet and sensing pole surfaces, thereby increasing stylus tip impedance and requiring a damping means to reduce vibrational problems. The pick-up cartridge provided by the invention solves the above problems.